Method for Selecting Antennas in a Wireless Networks

ABSTRACT

A method transmits data from a user equipment (UE) including a transceiver having a set of available antennas. The method selects a subset of antennas from the set of available antennas; and transmits the data by the transceiver using the subset of antennas. The selecting subset of antennas includes transmitting sounding reference signals (SRSs) according to specified times, frequencies, and antennas; and receiving, in response to the transmitting the SRSs, information indicative of a selection of the subset of antennas.

PRIORITY APPLICATION

This application is a Continuation of prior U.S. patent application Ser.No. 11/834,345, filed Aug. 6, 2007, by Mehta et al.

FIELD OF INVENTION

This invention relates generally to antenna selection in wirelessnetworks, and more particularly to selecting antennas in wirelessnetworks.

BACKGROUND OF THE INVENTION

OFDM

Orthogonal frequency division multiplexing (OFDM) is a multi-carriercommunication technique, which employs multiple orthogonal sub-carriersto transmit parallel data streams. Due to the relatively low symbol-rateon each of the sub-carriers, OFDM is robust to severe channelconditions, such as frequency attenuation, narrowband interference, andfrequency-selective fading. By prepending a cyclic prefix (CP) in frontof each symbol, OFDM can eliminate inter-symbol interference (ISI) whenthe delay spread of the channel is shorter than the duration of CP. OFDMcan also simplify frequency-domain channel equalization because themultiple sub-carriers are orthogonal to each other to eliminateinter-carrier interference (ICI).

OFDMA

When OFDM is combined with a multiple access mechanism, the result isorthogonal frequency division multiplexed access (OFDMA). OFDMAallocates different sub-carriers or groups of sub-carriers to differenttransceivers (user equipment (UE)). OFDMA exploits both frequency andmulti-user diversity gains. OFDMA is included in various wirelesscommunication standards, such as IEEE 802.16 also known as Wireless MAN.Worldwide Interoperability for Microwave Access (WiMAX) based on 802.16and the 3^(rd) generation partnership project (3GPP) long-term evolution(LTE), which has evolved from Global System for Mobile Communications(GSM), also use OFDMA.

SC-FDMA Structure in LTE Uplink

The basic uplink (UL) transmission scheme in 3GPP LTE is described in3GPP TR 25.814, v7.1.0, “Physical Layer Aspects for Evolved UTRA,”incorporated herein by reference. That structure uses a single-carrierFDMA (SC-FDMA) with cyclic prefix (CP) to achieve uplink inter-userorthogonality and to enable efficient frequency-domain equalization atthe receiver side. This allows for a relatively high degree ofcommonality with the downlink OFDM scheme such that the same parameters,e.g., clock frequency, can be used.

Antenna Selection

The performance of the system can be enhanced bymultiple-input-multiple-output (MIMO) antenna technology. MIMO increasessystem capacity without increasing system bandwidth. MIMO can be used toimprove the transmission reliability and to increase the throughput byappropriately utilizing the multiple spatially diverse channels.

While MIMO systems perform well, they may increase the hardware cost,signal processing complexity, power consumption, and component size atthe transceivers, which limits the universal application of MIMOtechnique. In particular, the RF chains of MIMO systems are usuallyexpensive. In addition, the signal processing complexity of some MIMOmethods also increases exponentially with the number of antennas.

While the RF chains are complex and expensive, antennas are relativelysimple and cheap. Antenna selection (AS) reduces some of the complexitydrawbacks associated with MIMO systems. In an antenna selection system,a subset of an set of the available antennas is adaptively selected by aswitch, and only signals for the selected subset of antennas areprocessed by the available RF chains, R1-063089, “Low cost training fortransmit antenna selection on the uplink,” Mitsubishi Electric, NTTDoCoMo, 3GPP RAN1#47, R1-063090, “Performance comparison of trainingschemes for uplink transmit antenna selection,” Mitsubishi Electric, NTTDoCoMo, 3GPP RAN1#47, R1-063091, “Effects of the switching duration onthe performance of the within TTI switching scheme for transmit antennaselection in the uplink,” Mitsubishi Electric, NTT DoCoMo, 3GPP RAN1#47,and R1-051398, “Transmit Antenna Selection Techniques for UplinkE-UTRA,” Institute for Infocomm Research (I2R), Mitsubishi Electric, NTTDoCoMo, 3GPP RAN1#43, R1-070524, “Comparison of closed-loop antennaselection with open-loop transmit diversity (antenna switching betweenTTIs),” Mitsubishi Electric, 3GPP RAN1#47bis, R1-073067, “Adaptiveantenna switching with low sounding reference signal overhead,”Mitsubishi Electric, 3GPP RAN1#49bis, R1-073068, “Impact of soundingreference signal loading on system-level performance of adaptive antennaswitching,” Mitsubishi Electric, 3GPP RAN1#49bis, all incorporatedherein by reference.

Signaling and Protocol Design for Antenna Selection

A signaling format for indicating a selected antenna is described inR1-070860, “Closed loop antenna switching in E-UTRA uplink,” NTT DoCoMo,Institute for Infocomm Research, Mitsubishi Electric, NEC, Sharp,Toshiba Corporation, 3GPP RAN1#48, incorporated herein by reference. Inorder to indicate one antenna out of two possible antennas (A and B),that scheme uses 1 of bit information, either explicitly or implicitly,into an “uplink scheduling grant” message, which indicates the antennaselection decision, 0 means antenna A, and 1 indicates antenna B.

In the prior art, antenna selection is typically performed using pilotsignals. Furthermore, antenna selection has been performed only forsmall-range indoor wireless LANs (802.11n), and where only a single useris on a wideband channel at any one time, which greatly simplifiesantenna selection.

In the prior art, sounding reference signals (SRS) and data demodulation(DM) reference signals are only used for frequency dependent scheduling.

A protocol and exact message structure for performing antenna selectionfor large-range, outdoor OFDMA 3GPP networks is not known at this time.It is desired to provide this protocol and message structure forperforming antennas selection for an uplink of an OFDMA 3GPP wirelessnetwork.

SUMMARY OF THE INVENTION

One embodiment of invention discloses a method for transmitting datafrom a user equipment (UE) including a transceiver having a set ofavailable antennas. The method selects a subset of antennas from the setof available antennas; and transmits the data by the transceiver usingthe subset of antennas. The selecting subset of antennas includestransmitting sounding reference signals (SRSs) according to specifiedtimes, frequencies, and antennas; and receiving, in response to thetransmitting the SRSs, information indicative of a selection of thesubset of antennas.

Usually, the SRS are transmitted in response to receiving informationindicative of the specific times, frequency and antennas. Also, thesubset of antennas can be selected by a base station based on thetransmitted SRSs, such that the UE receives the selection from the basestation.

Another embodiment discloses a user equipment (UE) forming at least partof a wireless network. The UE includes a set of available antennas; atleast one RF chain, wherein a number of available antennas of the UE isgreater than a number of RF chains; and a means for transmitting theSRSs according to specified times, frequencies, and antennas, and forreceiving, in response to the transmitting the SRSs, informationindicative of a selection of the subset of antennas, wherein the RFchain transmits data using the selected subset of antennas. In onevariation of this embodiment, the means for transmitting the SRS and forreceiving the information is a transceiver including a processor.

Yet another embodiment discloses a method for transmitting data from atransceiver having a set of available antennas and at least one RFchain, wherein a number of available antennas in the set is greater thana number of RF chains, wherein the transceiver is a part of a wirelessnetwork including a base station and a plurality of transceivers. Themethod includes steps of transmitting, to the base station, soundingreference signals (SRSs) according to specified times, frequencies, andantennas; receiving, from the base station in response to thetransmitting the SRSs, information indicative of a selection of thesubset of antennas; and transmitting the data to the base station usingthe subset of antennas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of a wireless network according to anembodiment of the invention;

FIG. 1B is a block diagram of a frame according to an embodiment of theinvention;

FIG. 1C is a method for selecting antennas according to an embodiment ofthe invention;

FIG. 2A is a block diagram of sub-frame structure according to anembodiment of the invention;

FIG. 2B is a block diagram of time-slot structure according to anembodiment of the invention;

FIG. 2C is a block diagram of a resource block according to anembodiment of the invention;

FIG. 3 is a block diagram of the Level-A registration signalingprocedure according to an embodiment of the invention;

FIG. 4 is a block diagram of legend descriptions used for FIGS. 5A to 8Baccording to embodiments of the invention;

FIGS. 5A to 8B are block diagrams of protocols for Option1 signalingaccording to embodiments of the invention;

FIG. 9 is a block diagram of legend description used for FIGS. 10A to13B according to embodiments of the invention; and

FIGS. 10A to 13B are block diagrams of protocols for Option2 signalingaccording to embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

LTE System Overview

FIG. 1 shows the general structure of an OFDMA 3GPP LTE wireless networkaccording to an embodiment of the invention. Multiple user equipments(UEs) or transceivers 111-113 communicate with a base station 110. Itshould be understood that the base station also operates as atransceiver. However, hereinafter, reference to transceivers means UE,unless specified otherwise. It should be noted that invention can alsobe used with SC-FDMA and OFDM networks.

The base station is called an evolved Node B (eNodeB) in the 3GPP LTEstandard. The eNodeB 110 manages and coordinates all communications withthe transceivers in a cell using connections 101, 102, 103. Eachconnection can operate as a downlink from the base station to the UE oran uplink from the UE to the base station. Because the transmissionpower available at the base station is orders of magnitude greater thanthe transmission power at the UE, the performance on the uplink is muchmore critical.

To perform wireless communication, both the eNodeB and the transceiversare equipped with at least one RF chain and one antenna. Normally, thenumber of antennas and the number RF chains are equal at the eNodeB. Thenumber of antennas at the base station can be quite large, e.g., dozens.However, due to the limitation on cost, size, and power consumption, UEtransceivers usually have less RF chains than antennas 115. The numberof antennas available at the UE is relatively small, e.g., two or four,when compared with the base station. Therefore, antenna selection asdescribed is applied at the transceivers. However, the base station canalso perform the antenna selection as described herein.

Generally, antennas selection selects a subset of antennas from a set ofavailable antennas at the transceivers.

LTE Frame Structure

FIG. 1B shows the basic structure of a 10 ms frame 200 according to anembodiment of the invention. The horizontal axis indicates time and thevertical axis indicates frequency. The frame includes ten 1 mssub-frames 210 in the time domain. The frame is also partitioned intofrequency bands 220, e.g. fifty. The number of bands depends on thetotal bandwidth of the channels, which can be in the ranges of severalmegaHertz. Each sub-frame/band constitutes a resource block, see inset230 and FIG. 2C for details.

Method

FIG. 1C shows the basic method for antenna selection according to anembodiment of the invention. The base station 110 specifies times andfrequencies to transmit sounding reference signals (SRSs) 161, andspecifies which antennas of the set of available antennas to use totransmit the SRSs for the specified times and frequencies. Thetransceiver 101 transmits the SRSs 161 according to the specified times,frequencies, and antennas 151.

The base station selects 170 a subset of antennas 181 based on thereceived SRSs 161. The base station then indicates 180 the selectedsubset of antenna 181 to the transceiver. Subsequently, the transceiver101 can transmit 190 data 191 using the selected subset of antennas 181.The transceiver can also use the same subset of antennas for receivingdata from the base station.

LTE Frame Structure

FIG. 2A shows a general structure of a sub-frame according to anembodiment of the invention. In 3GPP LTE, the transmission time of aframe is partitioned into TTIs (transmission time interval) 201 ofduration 1.0 ms. The terms ‘TTI’ and ‘sub-frame’ are usedinterchangeably. The frame is 10 ms long, which includes 10 TTIs. TheTTIs include time-slots 202.

FIG. 2B shows a general structure of a time-slot according to anembodiment of the invention. As described above, the TTI is the basictransmission unit. One includes two equal length time-slots 202 eachwith a duration of 0.5 ms. The time-slot includes seven long blocks (LB)203 for symbols. The LBs are separated by cyclic prefixes (CP) 204. Intotal, one TTI comprises fourteen LB symbols. It should be noted thatthe invention is not limited to a specific frame, sub-frame, ortime-slot structure.

FIG. 2C shows the details of one resource block (RB) 230 during one TTI201 according to an embodiment of the invention. The TTI is partitioned,in time, into fourteen LBs 203. Each LB can carry a symbol. The entiresystem bandwidth, e.g., of 5 MHz or 10 MHz or 20 MHz, is partitioneddivided into sub-carriers 205 at different frequencies. Groups of twelvecontiguous sub-carriers, as shown, within one TTI are called resourceblocks (RBs). For example, 10 MHz of bandwidth within 1 TTI mightinclude fifty RBs in the frequency domain. The two shaded LBs 210, i.e.,the 4^(th) and 11^(th) LBs, carry data demodulation (DM) referencesignals (RS) that are known to the receiver. The DM RS enables thereceiver to estimate the channel state of the RBs assigned to thetransceiver and coherently demodulate the unknown data carried in theother LBs. That is, in the prior art, DM reference signals are only usedfor channel estimation prior to data demodulation. For clarity the CPsare not shown in FIG. 2C. It should be noted that the invention is notlimited to a specific number of LBs during the TTI or the location ofthe DM RSs in the TTI. According to one embodiment of the invention, theDM reference signal is also used for antenna selection.

Sounding Reference Signal (SRS)

Except for the 4^(th) and the 11^(th) LBs, the other LBs are used fortransmitting control and data signals, as well as uplink soundingreference signals (SRS). For instance, the first LB can carry the SRS.The SRS is usually a wideband or variable bandwidth signal. The SRSenables the base station to estimate the frequency response of theentire system bandwidth or a portion thereof. This information enablesthe base station to perform resource allocation such as uplinkfrequency-domain scheduling.

According to the embodiment of the invention, the SRSs are also used forantenna selection.

Another option considered for 3GPP LTE is a frequency-hopping (FH) basedSRS. Specifically, a hopping SRS, with a bandwidth smaller than thesystem bandwidth, is transmitted based on a pre-determined hoppingpattern. The hopped SRSs, over multiple transmissions, span a largeportion of the system bandwidth or even the entire system bandwidth.With frequency hopping the probability that transceivers interfere witheach other during sounding is decreased.

In 3GPP LTE, the eNodeB can enable and disable SRS transmission by theUE transceiver. Moreover, when antenna selection is enabled, the eNodeBcan specify the SRS parameters to the transceiver, includingtransmission bandwidth, starting or ending bandwidth position,transmission period, cyclic shift hopping sequence, transmissionsub-frame, repetition factor for indicating the density of the pilotsubcarriers in the SRS LB, duration of SRS transmission, symbol positionof SRS within a sub-frame, and hopping SRS related parameters, amongothers. Furthermore, to support antenna selection by using SRS, the sameSRS is used by all antennas. Thus, the eNodeB knows in advance, whichantenna is sending the SRS.

In one embodiment of the invention, we describe a format and protocolfor antenna selection by using SRS in the 3GPP LTE wireless network.When SRS are used for antenna selection, the SRS is called an antennaselection SRS (A-SRS). Otherwise, the SRS is called a regular SRS(R-SRS). Making the A-SRS protocol compatible with the R-SRS protocolensures that extra signaling overhead associated with A-SRS is as low aspossible.

Signaling for Antenna Selection

In general, our invention comprises three levels of messages, namely,Level-A registration signaling, Level-B slow signaling, and Level-C fastsignaling, all or some of which can be used for antenna selection. Asummary of the possible signaling messages for enabling antennaselection is shown in Table 1A and Table 1B, where the two tablescorrespond to two slightly different signaling options: Option1 andOption2.

The major difference between Option1 and Option2 is the “SRS start/stop”message. The “SRS start/stop” is a Level-B message in Option1 and aLevel-C message in Option2. In the following, we first describe Option1in details. Then, we describe Option2 by mainly focusing on thedifferences between the two options.

TABLE 1A Signaling messages for antenna selection [Option1] Message SizeField Layer (bits) Comment UL Level-A: L3 [1] The UE notifies eNodeB ifUE Registration supports uplink antenna selection. DL Level-A: L3 [1]The eNodeB notifies UE if eNodeB Registration supports antennaselection. Level-B: L3 [FFS] SRS start/stop. Slower b) Enable/disableA-SRS, and set up Signaling A-SRS parameters when AS is enabled.Level-C: L1 [1] Antenna selection decision about Faster which subset ofantennas UE should Signaling use for transmission. In the above table,“FFS” means “for further specification.

TABLE 1B Signaling messages for antenna selection [Option2] Message SizeField Layer (bits) Comment UL Level-A: L3 [1] The UE notifies eNodeB ifUE Registration supports uplink antenna selection. DL Level-A: L3 [1]The eNodeB notifies UE if eNodeB Registration supports antennaselection. Level-B: L3 [FFS] Enable/disable A-SRS, and set up SlowerA-SRS parameters when AS is Signaling enabled. Level-C: L1 [3] SRSstart/stop. Faster b) Antenna selection decision about Signaling whichsubset of antennas UE to use for transmission (and reception).

Signaling Description for [Option1]

As shown in Table 1A, the Level-A registration signaling indicateswhether both the transceiver and the eNodeB support uplink (UL) antennaselection. If the eNodeB does not support antenna selection but thetransceiver does, the transceiver can use open-loop antenna selection,which does not require any support from the eNodeB. This information isexchanged between the transceiver and the eNodeB at the beginning of thecommunications, for example, when the transceiver registers with thewireless network upon entry.

Level-B is a layer 3 (or radio resource control (RRC) layer) signalingthat is used to set up AS training parameters for the SRS. Level-B is aslow form of signaling that is used infrequently. The eNodeB usesLevel-B signaling to stop and start the transceiver to send the A-SRS,or to change the A-SRS parameters.

Level-C is fast signaling that is used by the eNodeB to communicate tothe transceiver its antenna selection decisions, and to enable theantenna selection to track short-term variations due to channel fading.

In the uplink (UL), only the Level-A message is needed from thetransceiver to notify the eNodeB of its capability of supporting AS. Inthe downlink (DL), some or all of the three levels of messages may benecessary.

Level-A Signaling

The Level-A registration signaling is used to indicate if both thetransceiver and the eNodeB support uplink antenna selection. Thisinformation is exchanged between the transceiver and the eNodeB when thetransceiver enters the network and before beginning data communications.

The basic procedure between transceiver and eNodeB to exchange theregistration information is shown in FIG. 3. In the uplink (UL), 1-bitinformation is required for the UE transceiver 301 to notify the basestation eNodeB 302 whether it is an antenna selection capabletransceiver, or not. Similarly, in the downlink (DL), 1-bit informationis needed for the eNodeB 302 to inform the transceiver about itscapability to support uplink transmit AS.

In one embodiment of the invention, we include the 1-bit uplink Level-Asignaling in the “UE capability information” message 303 sent by thetransceiver, and include the 1-bit downlink Level-A signaling into “UEcapability information confirm” message 304 sent by the eNodeB.

The “UE capability information” contains a “radio access capability”field. The “radio access capability” field further comprises a “physicalchannel capability” field. Similar to the “UE MIMO support” alreadyincluded in the “physical channel capability”, a 1-bit “UE AS support”field is added into the “physical channel capability” to indicate theUE's antenna selection capability.

It is also possible to include the above Level-A signaling informationinto other messages. Depending on how the radio resource control (RRC)protocol is designed in 3GPP LTE, the Level-A signaling can be adjustedaccordingly.

Level-B Signaling

The frame structure for Level-B message [Option1] is shown in Table 2.The Level-B signaling is used to set up AS parameters. This informationis required when the eNodeB requests the transceiver to start or stopsending the SRS, or to change A-SRS parameters. R-SRS and A-SRS sharethe same Level-B signaling message, except that two fields (i.e., “A-SRSEnable” and “Period2” shown in boldface in Table 2) are for A-SRS. Itshould be noted that all the message format descriptions provided hereinare only examples and variations are possible within the scope of thisinvention.

TABLE 2 Frame structure for Level-B message [Option1] Size Field (bits)Comment SRS Start/Stop [1] Request to start (when set to 1) or stop(when set to 0) sending SRS. A-SRS Enable [1] A-SRS is enabled (when setto 1) or R-SRS is enabled (when set to 0). Periodic/Adaptive [1]Indicates whether the SRS is performed periodically (when set to 1,until told to stop) or adaptively (when set to 0, one- shot SRS). BW &Position [FFS] The bandwidth (in terms of number of RBs) and thestarting position (in terms of RB index) for the SRS. Start Sub-frame[FFS] The index of the subframe within a radio frame that the UE startssending the SRS. Symbol Position [FFS] The index of the LB within asub-frame at which the SRS is located (SRS is not necessary at the1^(st) LB of a sub-frame). Period1 [FFS] The interval (in terms ofnumber of TTIs) between two consecutive SRSs. This value does not matterfor non- hopping adaptive R-SRS. Period2 [FFS] The interval (in terms ofnumber of SRSs) between two consecutive A-SRSs and pattern oftransmission. Hopping Related [FFS] Indicates hopping relatedinformation Fields such as number of hops, hopping pattern, etc.

The field “SRS Start/Stop”, when set to 1, indicates the request fromthe eNodeB to start sending SRS (for both A-SRS and R-SRS cases).Otherwise, when this bit is set to 0, then the eNodeB requests thetransceiver to stop sending SRS.

The field “A-SRS Enable”, when set to 1, indicates that the A-SRS isenabled. Then, all the other fields of this message are used for settingup A-SRS parameters. The meaning of each field is described in the“Comment” column of Table 2. If “A-SRS Enable” is set to 0, then R-SRSis enabled. Thus, the other fields (except “Period2”) of this messageare used for setting up R-SRS parameters. By sharing parameter fieldswith R-SRS, the overhead for enabling A-SRS is low.

The field “Period1” indicates the interval (in terms of number of TTIs)between any two consecutive SRSs, which is used for both A-SRS andR-SRS. The field “Period2”, on the other hand, is only used for periodicA-SRS, which indicates the interval between two consecutive A-SRSs aswell as the pattern of transmission of the A-SRS. By using “Period2”,the eNodeB can dynamically adjust the portion of the SRSs that are sentfrom the unselected antenna, achieving a tradeoff between theperformance and the antenna-switching overhead. The value “Period2”should be no less than 2. If Period2=2, then the SRS is alternativelytransmitted from the selected antenna and the unselected antenna.

Upon receiving the Level-B message, the transceiver first checks the“SRS Start/Stop” field. If “SRS Start/Stop=0”, then the transceiverstops sending SRS. The other fields of this message are omitted.Otherwise, if “SRS Start/Stop=1”, then the transceiver is told to startsending SRS according to the format (e.g., either A-SRS or R-SRS; eitherperiodic or adaptive, etc) defined in the parameter list.

A number of variations for the structure of the above Level-B messageare possible. First, all the fields need not be sent together at thesame time. Depending on the function categories, the Level-B messagemight be split into sub-messages and sent separately. Second, the 1-bitfield “A-SRS Enable” can be inside another field of this message.Depending on how R-SRS signaling is designed in 3GPP LTE, A-SRSsignaling may need to be adjusted accordingly in compliance with R-SRS.

Level-C Signaling

The frame structure for Level-C message [Option1] is shown in Table 3.The Level-C fast signaling message is used to signal the transceiverabout which antenna to use for data transmission. For selecting oneantenna out of two possible candidates, a 1-bit information fieldsuffices. One option is to include this 1-bit information in the “uplinkscheduling grant” message. It should be noted that all the messageformat descriptions provided herein are only examples.

TABLE 3 Frame structure for Level-C message [Option1] Size Field (bits)Comment Resource ID (UE or [8-9] Indicates the UE (or group of UEs)assignment group specific) for which the grant is intended Resource FFSIndicates which uplink resources, assignment localized or distributed,the UE is allowed to use for uplink data transmission. AS [1] Indicatesthe decision on which Decision subset of the antennas is selected fordata transmission Duration of [2-3] The duration for which the assign-assignment ment is valid. The use for other purposes is FFS. TFTransmission FFS The uplink transmission parameters parameters(modulation scheme, payload size, MIMO-related information, etc) the UEshall use.

The “uplink scheduling grant” is used by the eNodeB to make an uplinkscheduling decision for a transceiver specified by the “ID” field. Inthe “resource assignment” field, the eNodeB notifies the transceiverwhich RBs are assigned for its data transmission. The 1-bit antennaselection decision can be created in this field. Thus, when antennaselection is enabled, the “resource assignment” field indicates a jointscheduling and antenna selection decision.

The “AS Decision” bit, when set to 1, indicates that the transceivershould switch to a different transmit antenna to transmit data. If thisfield is set to 0, then the transceiver uses the same antenna totransmit data. Upon receiving this message, the transceiver continues touse the same antenna, or switches to a different antenna, according tothe decision made by the eNodeB. The above method corresponds to a“relative antenna index” based approach. That is, the eNodeB does notknow exactly which antenna is used. Instead, the eNodeB just notifiesthe transceiver to either “switch” or “not switch” the subset ofselected antennas. It is also possible to use an “absolute antennaindex” based approach to indicate the antenna selection decision, wherethe eNodeB notifies the transceiver either to use the antenna or the2^(nd) antenna, or otherwise designated subsets.

It should be noted that it is also possible to include the AS decisioninformation in other fields (e.g., “TF” field) of the uplink schedulinggrant message, or even inside other message.

Signaling Description for [Option2]

As shown in Table 1B, [Option2] is similar to [Option1] except for the“SRS start/stop” message, which is a Level-B message in [Option1] and aLevel-C message in [Option2]. The advantage of [Option2] is that theSRSs (both R-SRS and A-SRS) can be configured quickly to start/stop(especially stop) for granting a priority to other transceivers.However, the disadvantage is the slightly larger payload of the Level Cmessages.

In [Option1], the A-SRS parameters are combined together with SRSrequest (either to start or stop). In [Option2], the A-SRS parametersand SRS request are sent separately. Therefore, in [Option2], theLevel-B message does not include “SRS start/stop” field (i.e., the firstfield in Table 2). Meanwhile, 2 bits are added to the Level-C message inorder to achieve the same “SRS start/stop” function. Thus, a total of 3bits are required for Level-C message in [Option2].

The fields that constitute a Level-C message [Option2] are shown inTable 4. The Level-C message is used to indicate A-SRS request start orstop and antenna selection decision. In one embodiment of the invention,we include this 3-bit information in “uplink scheduling grant” message.It should be noted that all the message format descriptions providedherein are only examples.

TABLE 4 Frame structure for Level-C message [Option2] Size Field (bits)Comment Resource ID (UE or [8-9] Indicates the UE (or group of UEs)assignment group for which the grant is intended specific) Resource FFSIndicates which uplink resources, assignment localized or distributed,the UE is allowed to use for uplink data transmission. SRS Start [1]Request to start (when set to 1) sending SRS. Otherwise (when set to 0),keep current status. SRS Stop [1] Request to stop (when set to 1)sending SRS. Otherwise (when set to 0), keep current status. AS [1]Indicates which transmit antenna is Decision selected for UL datatransmission Duration [2-3] The duration for which the assignment of isvalid. The use for other purposes, assignment e.g., to controlpersistent scheduling, ‘per process’ operation, or TTI length, is FFS.TF Transmission FFS The uplink transmission parameters parameters(modulation scheme, payload size, MIMO-related information, etc) the UEshall use. If the UE is allowed to select (part of) the transportformat, this field sets determines an upper limit of the transportformat the UE may select.

Upon receiving the Level-C message, the transceiver checks “SRS start”and “SRS stop” bits. If either bit is set to 1, then this messagecontains the eNodeB's request to either start or stop sending SRS. When“SRS start=1”, the transceiver is told to start sending SRS based on theLevel-B parameters. It is assumed that the transceiver has alreadyobtained the Level-B parameters in advance in a separate message (ortransceiver can store a set of default Level-B parameters). When “SRSstop=1”, then the transceiver stops sending the SRS. However, it ispossible that both bits are 0. In this case, the transceiver keeps itscurrent SRS status, until either “SRS start” or “SRS stop” is set to 1.

The transceiver also checks the “AS Decision” bit. The responses to “ASDecision” bit are the same as [Option1] at transceiver.

It should be noted that it is also possible to include “SRS Start” and“SRS Stop” information inside another field (e.g., “TF” field) of theuplink scheduling grant message, or even inside other message. Also, the“SRS Start” and “SRS Stop” can be at a separate message from the “ASDecision”. In this case, the “SRS Start” and “SRS Stop” can be combinedtogether into 1 bit, just as that in [Option1]. However, A-SRS and R-SRSshare the same SRS request. Depending on how R-SRS signaling will bedesigned in 3GPP LTE, A-SRS signaling may need to be adjustedaccordingly in compliance with R-SRS.

Protocol for Antenna Selection

In one embodiment of the invention, our protocol utilizes the soundingreference signal (SRS) 161 for uplink transmit antenna selection,R1-073067, “Adaptive antenna switching with low sounding referencesignal overhead,” Mitsubishi Electric, 3GPP RAN1#49bis, R1-073068,“Impact of sounding reference signal loading on system-level performanceof adaptive antenna switching,” Mitsubishi Electric, 3GPP RAN1#49bis.The antenna switching is performed within a TTI, but we do not precludebetween TTI switching, R1-063089, “Low cost training for transmitantenna selection on the uplink,” Mitsubishi Electric, NTT DoCoMo, 3GPPRAN1#47, R1-063090, “Performance comparison of training schemes foruplink transmit antenna selection,” Mitsubishi Electric, NTT DoCoMo,3GPP RAN1#47, and U.S. patent application Ser. No. 11/620,105, “Methodand System for Antenna Selection in Wireless Networks” filed by Mehta etal. on Jan. 5, 2007, incorporated herein by reference.

In terms of functionality, the protocol is flexible and applicable todifferent antenna selection scenarios. First, both periodic antennaselection and adaptive antenna selection are supported. In particular,the protocol can switch between different periodic AS (with differentsounding intervals), or between different adaptive AS (with differentsounding intervals), or between periodic and adaptive AS, or even allowthem together, as dictated by the eNodeB. Second, both non-hopping SRSbased and hopping SRS based antenna selections are supported. Theprotocol can also switch between them as dictated by eNodeB. Third, theprotocol supports antenna selection based on different SRSs, includingwideband SRS, variable bandwidth SRS, and narrow-band SRS. Fourth, theprotocol supports antenna selection for packet retransmission in bothasynchronous HARQ and synchronous HARQ modes.

The current protocol focuses on 1 out of 2 antenna selection, while theextension to multiple antenna selection is possible with a cost ofadditional signaling overhead.

Protocol Description for [Option1]

FIG. 4 shows the legend for protocol [Option1], which is used for theFIG. 5A to FIG. 8B, according to an embodiment of the invention. Thelegends are intended to simplify the details of the otherwise complexdrawings. The legends are Wideband or variable bandwidth SRS 401,Narrow-band hopping SRS 402, Data block (sub-frame) if no SRS is sent atthe same TTI 403, Data block (sub-frame) if SRS is sent at the same TTI404, No data to send in a TTI 405, Level-B slower signaling: SRSparameters & SRS request 406, and Level-C faster signaling: AS &scheduling decision 407.

For clarity Level-A signaling exchange is omitted herein. It should benoted that all the protocols herein are only examples.

No Frequency Hopping—Wideband SRS and Variable BW SRS

Periodic SRS: FIGS. 5A and 5B show the protocol illustration fornon-hopping periodic A-SRS and R-SRS, respectively. As shown in FIG. 5A,at the 1^(st) TTI of a frame, the eNodeB sends a set of SRS parameters501, which includes an “SRS Start” request. The detailed parameters arelisted at the bottom-left corner 502 in FIG. 5A. The transceiverreceives this request at the 2^(nd) TTI 503, and gets ready to send SRSas per the parameters. Based on the parameter 502, at the 3^(rd) TTI(i.e., Start_Subframe=3), the transceiver starts sending SRS 504, andwill periodically send the SRS from the two antennas at every TTI (i.e.,Period1=1, until told to stop). Based on received SRS 504, the eNodeBcan make a joint scheduling and AS decision 505. The transceiverreceives the decision in the 5^(th) TTI 506, and will react with acertain TTI delay. The decision can be either a resource blockassignment or an antenna selection decision or both. Note that in someTTI 507, there is no data to send, but the transceiver still needs tosend SRS periodically as required. Also note that the eNodeB can makedecision 508 at any time, not necessary periodically.

Because “Period2=3”, one out of every 3 SRSs is sent from the unselectedantenna. As shown in FIG. 5A, the SRS 509 at the 5^(th) TTI, the SRS 510at the 8^(th) TTI, and the SRS 511 at the 1^(st) TTI of the next frame,are sent from the unselected antenna, while the rest SRSs are sent fromthe selected antenna.

For comparison purpose, FIG. 5B shows the protocol for non-hoppingperiodic R-SRS, which can be seen from the parameter 512 with “ASEnable=0”. The difference is that the decision from eNodeB is only ascheduling decision, not an antenna switching decision. The SRSs aresent periodically every 2 TTIs (“Period1=2”). The “Period2” field is nouse for R-SRS case.

In FIGS. 5A and 5B, the parameter “Num_Hops=1” means that the entirebandwidth is covered by 1 hop. That is, no frequency hopping isinvolved. If “Num_Hops>1”, then frequency hopping is applied for SRS.

It should be noted that in the example protocols, we assume a certaindelay for the eNodeB to make AS and scheduling decision, and a certaindelay for the transceiver to react to the eNodeB's instruction. Thedelay depends on the standard specification, and the values providedherein are only examples.

Adaptive SRS: FIGS. 6A and 6B show the protocol for non-hopping adaptiveA-SRS and R-SRS, respectively. Compared to the case with periodicantenna selection where the SRSs are sent periodically (until told tostop), adaptive SRS is a “one-shot” SRS transmission as per the eNodeB'srequest. For the A-SRS shown in FIG. 6A, two SRSs are sent by the twoantennas successively, with the interval determined by the “Period1”field in the parameter list. Similar to the periodic case, the eNodeBmakes scheduling and/or AS decision based on the received A-SRSs. Forthe R-SRS shown in FIG. 6B, only one SRS is sent by the transmitantenna. Therefore, the “Period1” field is of no use in this case.

Frequency Hopping—Narrow-band SRS

Periodic SRS: FIGS. 7A and 7B show the protocol for hopping periodicA-SRS and R-SRS, respectively. For example purposes, we assume that theentire bandwidth is covered by 2 hops (Num_Hops=2), and each narrow-bandSRS spans half of the available bandwidth. As shown in FIG. 7A, in orderto make each of the two antennas sound the entire bandwidth, a total of4 SRSs are required in each sounding cycle. The interval between twoconsecutive SRSs is determined by “Period1” field of the parameter list701 (it is set to 1 in the figure as an example). Similar to thenon-hopping case, because “Period2=3” in the parameter list 701, one outof every 3 SRSs is sent from the unselected antenna. Specifically, theSRS 702 at the 5^(th) TTI, the SRS 703 at the 8^(th) TTI, and the SRS704 at the 1^(st) TTI of the next frame, are sent from the unselectedantenna, while the rest SRSs are sent from the selected antenna. TheeNodeB can make a scheduling and AS decision each time when it receivesan A-SRS.

As shown in FIG. 7B, when “AS Enable=0” the transceiver transmits R-SRSfrom only one antenna. A total of 2 SRSs are required in each cycle tosound the entire bandwidth. Based on the received SRSs, the eNodeB makesscheduling decisions without any antenna selection.

Adaptive SRS: FIGS. 8A and 8B show the protocol for hopping adaptiveA-SRS and R-SRS, respectively. As shown in FIG. 8A, upon receiving therequest 801 from the eNodeB, the transceiver sends a total of 4 SRSs.Based on one or more SRSs, the eNodeB can make AS and schedulingdecisions at any time. In FIG. 8B, because R-SRS is employed (ASEnable=0), a total of 2 SRSs is sent by the transceiver for the eNodeBto make scheduling decisions. The interval between the 2 SRSs isdetermined by the “Period1” field.

Protocol Description for [Option2]

FIG. 9 shows the legend for protocol [Option2], which is used for theillustrations from FIG. 10A to FIG. 13B. The legends are Wideband orvariable bandwidth SRS 901, Narrow-band hopping SRS 902, Data block(sub-frame) if no SRS is sent at the same TTI 903, Data block(sub-frame) if SRS is sent at the same TTI 904, No data to send in a TTI905, Level-B slower signaling: SRS parameters, 906, Level-C fastersignaling: SRS request (to start) 907, and Level-C faster signaling: AS& scheduling decision 908. For clarity Level-A signaling exchange isomitted herein. It should be noted that all the protocol illustrationsprovided herein are only examples.

Similar to FIGS. 5A to 8B, FIGS. 10A to 13B show the same SRS scenarioswhen the signaling is set to [Option2], respectively. Recall that in[Option2], the Level-B SRS parameters are sent separately from theLevel-C SRS start/stop request. Also, it is assumed that when thetransceiver receives an SRS request, the transceiver has obtained of therequired SRS parameters in a separate Level-B message (or uses defaultvalues for the parameter values it has not received yet). For instance,as shown in FIG. 10A, the eNodeB can send the SRS parameters 1001 andthe SRS request 1002 at the same TTI. As shown in FIG. 11A, the SRSparameter 1101 can also be sent before the SRS request 1102. The otherprocedures are the same as [Option1].

Switching Between Different SRS Patterns

In order to switch between different SRS patterns (e.g., periodic vs.adaptive, hopping vs. non-hopping, etc), a Level-B slower signaling fromthe eNodeB to the transceiver is required for both [Option1] and[Option2] to set up different SRS parameters. In addition, for[Option2], an “SRS Start” from the eNodeB to the transceiver is alsoneeded.

It should be noted that under the current protocol, the eNodeB canpossibly send SRS request and the AS decision in the same TTI. It shouldalso be noted that when the number of hops (i.e., the “Num_Hops” fieldin parameter list) is larger than 2, different hopping patterns thatjointly span the frequency-space domain can be designed. The pattern canbe either signaled by the eNodeB or is chosen from a pre-determined set.In FIGS. 5A to 8B and FIGS. 10A to 13B, only the procedure of “SRSStart” is shown. The procedure of “SRS Stop” is not shown in thesefigures, and is sent in a similar manner.

Antenna Selection Protocol for HARQ

Asynchronous HARQ

If the system operates in an asynchronous HARQ mode, then the eNodeBindicates to the transceiver when, which RBs, and with what MCS(modulation and coding scheme) to retransmit the packet. Because theeNodeB has complete control over the packet retransmission inasynchronous HARQ, the eNodeB can also signal the transceiver whether ornot to switch the antenna for retransmission. It can also indicate tothe transceiver to send an aperiodic or a periodic A-SRS. In this case,the eNodeB makes a joint AS and scheduling decision for theretransmitted packet, similar to that for a normal packet.

Synchronous HARQ

If the system operates in synchronous HARQ mode, then the transceiverknows a priori exactly when to retransmit the packet when it does notreceive an ACK from the eNodeB after a pre-specified number of TTIs. Inthis case, the transceiver uses the same resource block (RB) and sameMCS for the retransmission. Because the transceiver has complete controlover the packet retransmission in synchronous HARQ, wheneverretransmission occurs, the transceiver can automatically switch toanother subset of antennas to retransmit (using the same RB and MCS).This is to avoid the scenario that the channel quality of the previouslyselected subset of antennas is poor.

EFFECT OF THE INVENTION

The embodiments of the invention provide signaling and protocol forantenna selection in the uplink of OFDM 3GPP wireless network betweenthe transceiver and the eNodeB.

Although the invention has been described by way of examples ofpreferred embodiments, it is to be understood that various otheradaptations and modifications may be made within the spirit and scope ofthe invention. Therefore, it is the object of the appended claims tocover all such variations and modifications as come within the truespirit and scope of the invention.

1. A method for transmitting data from a user equipment (UE) including atransceiver having a set of available antennas, the method comprising:selecting a subset of antennas from the set of available antennas; andtransmitting the data by the transceiver using the subset of antennas,wherein the selecting comprises: transmitting sounding reference signals(SRSs) according to specified times, frequencies, and antennas; andreceiving, in response to the transmitting the SRSs, informationindicative of a selection of the subset of antennas.
 2. The method ofclaim 1, wherein the SRS are transmitted in response to receivinginformation indicative of the specific times, frequency and antennas, 3.The method of claim 1, wherein the subset of antennas is selected by abase station based on the transmitted SRSs, such that the UE receivesthe selection from the base station.
 4. The method of claim 1, furthercomprising: transmitting antenna selection capability information fromthe transceiver to a base station; and receiving, in response totransmitting the capability information, a conformation of thecapability information.
 5. The method of claim 1, further comprising:performing the selecting periodically.
 6. The method of claim 1, furthercomprising: performing the selecting adaptively.
 7. The method of claim1, further comprising: performing the selecting based on hopping SRSs.8. The method of claim 1, further comprising: performing the selectingbased on wideband SRSs.
 9. The method of claim 1, further comprising:performing the selecting based on variable bandwidth SRSs.
 10. Themethod of claim 1, further comprising: performing the selecting based onnarrow-band SRSs.
 11. The method of claim 1, further comprising:receiving antenna selection parameters including one or combination oftransmission bandwidth, starting or ending bandwidth position,transmission period, cyclic shift hopping sequence, transmissionsub-frame, repetition factor for indicating a density of a pilotsubcarriers, a duration of the SRS transmission, symbol position of theSRS within a sub-frame, and hopping SRS related parameters.
 12. A userequipment (UE) forming at least part of a wireless network, comprising:a set of available antennas; at least one RF chain, wherein a number ofavailable antennas of the UE is greater than a number of RF chains; anda means for transmitting the SRSs according to specified times,frequencies, and antennas, and for receiving, in response to thetransmitting the SRSs, information indicative of a selection of thesubset of antennas, wherein the RF chain transmits data using theselected subset of antennas.
 13. The UE of claim 12, wherein the SRS aretransmitted in response to receiving information indicative of thespecific times, frequency and antennas,
 14. The UE of claim 12, whereinthe subset of antennas is selected by a base station based on thetransmitted SRSs, such that the UE receives the selection from the basestation.
 15. The UE of claim 12, wherein the means for transmitting theSRS and for receiving the information is a transceiver including aprocessor.
 16. A method for transmitting data from a transceiver havinga set of available antennas and at least one RF chain, wherein a numberof available antennas in the set is greater than a number of RF chains,wherein the transceiver is a part of a wireless network including a basestation and a plurality of transceivers, the method comprising:transmitting, to the base station, sounding reference signals (SRSs)according to specified times, frequencies, and antennas; receiving, fromthe base station in response to the transmitting the SRSs, informationindicative of a selection of the subset of antennas; and transmittingthe data to the base station using the subset of antennas.
 17. Themethod of claim 16, wherein the SRSs are transmitted in response toreceiving from the base station information indicative of specifictimes, frequency and antennas.